build: Java version 21

- Changed Java version for build actions

Author: h-man2

.github/workflows/maven.yml

@@ -15,7 +15,7 @@ jobs:
     - name: Set up JDK 15
       uses: actions/setup-java@v3
       with:
-        java-version: '15'
+        java-version: '21'
         distribution: 'adopt'
         cache: maven
     - name: Build with Maven

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
        - name: Set up JDK
          uses: actions/setup-java@v3
          with:
-           java-version: '15'
+           java-version: '21'
            distribution: 'adopt'
            cache: maven